But that's only what you think she is missing. She could have had a sister and they could have fought like cats and dogs and never been friends. To be honest, I've seen that more often than I've seen sisters get along great. So that is one regret I would not worry about!
No....
I get what you are saying, but I cannot buy into it with my DD/sisters/family. I have 4 sisters and yes, we fought like cats and dogs, and hated each other when we were 13, and stole each other's clothes and shoes, and hated how my mom babied one of us and always stuck up for another, and made excuses for the one, and went through our parents divorces on different sides of the issues and us older ones raised our little sisters when our mom left and hated every second of it....
And yet, we stood up for each other. And cried to each other after we fought. Lived through each of our ups and downs, and boyfriends and marriages and kids and our crazy (literally) mother and distant father, together. Planned bridal and baby showers until we never wanted to plan another one. Had Sweet 16 parties, 19 parties (we lived near Canada in the days before passports were required and the drinking age was 19!), and 21st birthdays, and bachelorette parties, and every other thing that sisters do - good and bad.
My daughter sees her mom (me) and aunts when we get together at our (at least) 2x-year "all in" weekends (all 5 of us and our brother, and our families, all together at one of our houses for the weekend - BEST WEEKENDS EVER!!!), and she sees what it is like having sisters. She knows that other than her, her brothers, and DH, my 4 favorite people in the entire world are my sisters. She often talks about it with me.
Ironically, every one of us had a boy first, then a girl (if we had a second child) and then a boy if there is a 3rd. Not one of the 5 of us us have 2 girls. We all wish, if we could change one thing, that our daughters had a sister. We just don't have the "hate" factor that some families have. I know it is possible, but not very likely, that my DD would have hated a sister.
But it's OK....I always wanted a brother (my half-brother was born when I was 14), and my DD has two. She is so comfortable around boys and I never was.
Families usually turn out exactly they way they are supposed to!